The present invention relates to a tapered roller bearing suitable for use in environments where lubricating oil flows into the bearing.
A tapered roller bearing comprises an inner ring formed with a radially outwardly facing raceway and including small-diameter flange and a large-diameter flange at the axial ends of the raceway, an outer ring formed with a radially inwardly facing raceway, a plurality of tapered rollers disposed between the raceways of the inner and outer rings, and a retainer retaining the tapered rollers. The retainer comprises a small-diameter annular portion, a large-diameter annular portion and a plurality of crossbars through which the small-diameter and large-diameter annular portions are coupled together. The adjacent crossbars define trapezoidal pockets having narrow and wide ends facing the small-diameter and large-diameter annular portions, respectively. Each tapered roller is received in one of the pockets with its small-diameter end facing the small-diameter annular portion and its large-diameter end facing the large-diameter annular portion.
When such tapered roller bearings are used to support power transmission shafts of differentials or transmissions in automotive vehicles, they are used with their lower portions dipped in an oil bath. When such tapered rollers rotate, oil forming the oil bath flows into the bearings as lubricating oil. Lubricating oil that has flown into a tapered roller bearing from its small-diameter end partially flows through a bearing space defined radially outwardly of the retainer along the raceway of the outer ring toward the large-diameter ends of the tapered rollers, and partially flows through a bearing space defined radially inwardly of the retainer along the raceway of the inner ring toward the large-diameter ends of the tapered rollers.
Among tapered roller bearings used in environments where lubricating oil flows thereinto, there are known ones in which cutouts are formed in each pocket of the retainer (see JP patent publications 9-32858A (FIG. 3) and 11-201149A (FIG. 2)). With this arrangement, lubricating oil flowing through the spaces radially inwardly and outwardly of the retainer passes through the cutouts, so that lubricating oil can smoothly flow through the bearing. In the arrangement of the former publication, as shown in FIG. 7A, each pocket 9 has a pair of cutouts 10d formed in the crossbars 8 defining each pocket 9 at their intermediate portions. In the arrangement of the latter publication, as shown in FIG. 7B, each pocket 9 has a pair of cutouts 10e formed in the small-diameter annular portion 6 and the large-diameter annular portion 7 so that lubricating oil flowing through the bearing space defined radially outwardly of the retainer 5 can smoothly flow into the bearing space defined radially inwardly of the retainer 5. The retainers of Comparative Examples subjected to the below-described torque measurement test have the same dimensions as the dimensions of the retainers shown in FIGS. 7A and 7B.
It has been discovered that the higher the rate of the amount of lubricating oil flowing through the bearing space defined radially inwardly of the retainer with respect to the amount of lubricating oil flowing through the bearing space defined radially outwardly of the retainer, the greater the torque loss. This is presumably for the following reasons.
Since there exists no obstacle on the radially inner surface of the outer ring, lubricating oil flowing into the bearing space defined radially outwardly of the retainer smoothly flows therethrough along the raceway of the outer ring toward the large-diameter ends of the tapered rollers and leaves the bearing. On the other hand, the flow of lubricating oil through the bearing space defined radially inwardly of the retainer tends to be stopped or slowed down by the large-diameter flange formed on the radially outer surface of the inner ring at the large-diameter ends of the tapered rollers. Lubricating oil thus tends to remain in the bearing space defined radially inwardly of the retainer. Thus, the greater the amount of lubricating oil flowing into the bearing space defined radially inwardly of the retainer, the greater the amount of lubricating oil remaining in the bearing. Lubricating oil remaining in the bearing increases the rotational resistance of the bearing and thus the torque loss.
An object of the present invention is to reduce the torque loss in a tapered roller bearing by reducing the rotational resistance resulting from lubricating oil flowing into the bearing.